Supercharging is the process of increasing the power of an internal combustion engine by compressing a portion of the air required for the combustion process before it reaches the combustion chambers of the cylinders. This is often accomplished using a device known as a turbocharger that is comprised of a compressor and a turbine arranged on a common shaft. The hot exhaust-gas flow from the cylinders is supplied to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor delivers and compresses the air supplied to it (known as charge air), as a result of which supercharging of the cylinders is obtained.
The configuration of the exhaust-gas turbocharging often poses difficulties, wherein it is basically sought to obtain a noticeable performance increase in all engine speed ranges. It is possible to design a turbine with a large cross section so as to be adapted to high engine speeds, that is to say high exhaust-gas flow rates. However, because large turbines possess a relatively large moment of inertia, their rotation is hampered during periods of low exhaust-gas flow rates (e.g., low engine speeds) and their ability to adjust in response to changes in engine speed is poor. It is possible for these disadvantages to be counteracted by reducing the size of the turbine cross section which then increases the pressure at the turbine and increases performance at low engine speeds. However, this approach has problems because the exhaust-gas back pressure upstream of the turbine increases with increasing exhaust-gas flow rates, whereby the charge exchange is adversely affected and fuel consumption is increased. This reduces performance at high engine speeds.
In an attempt to address the above-described effect, the torque characteristic of a supercharged internal combustion engine may be altered by means of multiple turbochargers arranged in parallel. Multiple turbines of relatively small turbine cross section are arranged in parallel, wherein the turbines are activated successively with increasing exhaust-gas flow rate, similarly to a sequential supercharging arrangement. The torque characteristic may also be advantageously influenced by means of multiple exhaust-gas turbochargers connected in series. By connecting two exhaust-gas turbochargers in series, of which one exhaust-gas turbocharger serves as a high-pressure stage and one exhaust-gas turbocharger serves as a low-pressure stage, the compressor characteristic map can advantageously be expanded, specifically both in the direction of smaller compressor flows and also in the direction of larger compressor flows.
Other attempts to alter the torque characteristic in the lower engine speed range include radial compressors that are equipped with a guide device which comprises blades and which is arranged downstream of the at least one impeller in the housing diffuser. One example approach is shown by U.S. Pat. No. 6,814,540 B2. Therein, the vanes of the diffuser of a centrifugal compressor are attached to a common ring which can be selectively rotated to move to the vanes in unison. A guide device of said type is also described for example in DE 603 07 571 T2, the guide device of which comprises a—preferably rotatable—ring which holds a multiplicity of pivotable guide elements.
However, the inventors herein have recognized potential issues with such systems. As one example, the ring is rotatable only in a limited angle range in order to adjust the guide elements in unison with one another. Additionally, a method utilizing multiple turbochargers in series or parallel can significantly increase the cost and the space required by the supercharging system.
In one example, the issues described above may be addressed by a method for an inexpensive exhaust-gas turbocharging arrangement. The internal combustion engine according to the disclosure is equipped with at least one exhaust-gas turbocharger. In relation to the provision of multiple exhaust-gas turbochargers, the provision of a single exhaust-gas turbocharger also has advantages with regard to weight. Furthermore, the space requirement of the supercharging apparatus in the engine bay is reduced. The method includes a revolving support within the compressor, such that the support together with guide blades can, like the at least one revolving impeller, be continuously rotated or continuously rotate for multiple revolutions about the shaft of the compressor when an electrical auxiliary drive provides the required drive power. By contrast to the impeller, which is connected rotationally conjointly to the compressor shaft, the support is however rotatable relative to the shaft of the compressor. In this way, the impeller of the compressor can perform well at high engine speeds while the revolving support of the guide blades can increase the torque characteristic of the engine at low engine speeds.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.